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An example of the level of detail needed for A2 case studies and a discussion of the Mount St Helens 1980 eruption.
Citation preview
Referred to as the event that
spawned the birth of Modern
volcanology as a science, May
the 18th 1980 is a day burned in
the memory of millions of scien-
tists, residents and observers.
This was the first time a volcano-
logical event was so well record-
ed, monitored and predicted, and
then broadcast around the world.
Important to scientists and stu-
dents alike as the only recent
case study iof a major acidic
eruption in an MEDC, the les-
sons learned from this cataclys-
mic eruption were far reaching,
and led to many advanced moni-
toring systems being installed on
other deadly volcanoes around
the world.
In early march, the first signs of
significant activity since 1840
were detected. Starting as a small
swarm of earthquakes around the
volcano. Within 48 hours from
noon on March 25th, over 174
quakes of magnitude 2.6 and
over were recorded. By the week
of the 18th of May, there were 8
magnitude 4 or higher quakes per
day.
For the next two months, the
North side of the mountain
swelled as magma was injected
into the chamber, pushing the
north face upwards and out-
wards. This
started to desta-
bilize the slope,
and numerous
small collapses
and small erup-
tions were ob-
served.
(eruption col-
umns under 3km high)
The United States Geo-
logical Survey (USGS)
had been on site since
the start of the activity.
A series of seismometer
and geodetic stations
(Geodesy is the study of
the shape of the earth)
were positioned around
the volcano.
By April the 3rd, the
governor had declared a state of
emergency and order the evacu-
ation of most of the citizens
within the immediate danger
zone. One infamous resident,
Mr. Harry Truman, was among
those who refused to leave his
property and disbelieved the
geologists warnings.
As the eruption continues in
small bursts and harmonic trem-
ors for the next month, the pub-
lic began to loose interest, and
evacuated residents exerted
pressure on geologists to allow
them back into the exclusion
zone on the 17th of May, a se-
cond trip back to houses for
possessions was planned for 10
O'clock the next morning.
At 8:32 that Sunday morning, a
Magnitude 5.1 tremor loosed
the north face and triggered a
massive landslide. The removal
of just under 3 Km3 of mass
above the magma chamber trig-
gered a massive eruption about
7 seconds after the slide. The
landslide was a significant vol-
ume of material, however, the
initial release of pressure creat-
ed a pyroclastic blast of molten
magma and other ejectiles that
moved at speeds of between
220km/hr at the start to over
650km/hr over 20 miles away
from the vent. The combina-
tion of the slide and flow
caused the lake level to be
raised by 90m, feeding the
new ash deposits with water
creating Lahars, and stripping
bare the 600 square KM of
surrounding pine forests.
This was the first time geolo-
gists had ever realized the a
volcanic blast did not neces-
sarily go straight upwards, but
can come laterally out of the
cone. For USGS Volcanolo-
gist David Johnston, pictured
left, this realization came too
late as he was directly in the
path of the blast.
The eruption continued until
October 1980, killing 57 peo-
ple and the effects were felt as
far away as Wales. Even today
the volcano is still rumbling,
but much has been learned that
aids in current prediction and
management around the
world.
Mt St Helens - What on Earth Happened? Nearly 30 years ago, Americas most beautiful volcano came to life after a 120 year period of dormancy in an explosive demonstration of earths terrifying power. This issue discusses the event, what effects the eruption had, how far on the road to recovery we are, and how much longer it will take. Most importantly this issue will question; can America cope with this disaster again?
The Huish Volcanologist
R I C H A R D H U I S H C O L L E G E 01/06/2009
Timeline:
March—EQ’s signal
awakening from a 123
year sleep
April—State of Emer-
gency and evacuation
of residents and tourists
May 18th—massive
landslide triggers the
first lateral blast ob-
served in history killing
57 people
May 18th 1980 1
The Primary Impacts 2
MSH Lahars 2
Long Term Recovery 3
Potential Hazards 4
Further Reading 4
Inside this issue:
The impacts of any geomorphologi-
cal event are split into primary and
secondary. The most significant pri-
mary impact in this case was the
blast, which at times crossed the
sonic boundary. The debris flow was
superseded by a gas cloud moving
slightly faster, the average tempera-
ture of these clouds is 1000 degrees.
Containing blocks the size of double
Decker buses, molten lava
and parts of the volcano
wall, this cloud instantly
vaporized water it came
into contact with and
carbonized all organic
matter.
The blast itself did not last longer than 30 seconds, but
within that time it had devastated areas as far away as
30km, and the extreme heat caused devastation much
further afield.
What the blast did, was to open up the throat of the
magma chamber, relieving pressure and causing mag-
ma from deeper sources to ruch into and recharge the
chamber. Once started, the volcano formed an eruption column
that reached 19km high within 10 minutes. This column fed other
flows that sped down the flanks, and volcanic bombs to fall fur-
ther from the vent which created pits almost 20m deep and send-
ing as almost 2km up into the air.
Fifty-seven people were killed and 200 homes, 27 bridges,
15 miles (24 km) of railways and 185 miles (300 km) of high-
way were destroyed
The eruption ejected more than 1 cubic mile (4 km³) of materi-
al. A quarter of that volume was fresh lava in the form of ash,
pumice, and volcanic bombs while the rest was fragmented,
older rock.
The removal of the north side of the mountain (13% of the
cone's volume) reduced St. Helens' height by about 1,313 feet
(400 m) and left a crater 1 to 2 miles (2 to 3 km) wide and
2,100 feet (640 m) deep with its north end open in a huge
breach. The Ash and subsequent 17 pyroclastic flows deposit-
ed ash in 11 US states. 4 Billion Board feet worth of timber
was destroyed, one of the defining factors in the low mortali-
ty rate was that as it was a Sunday, had it been any other day
of the week, 300 loggers would have been working in the
blast zone.
Environmentally the devastation was total within the baslt
zone, for 30km around the main vent, the thermal blast
seared all life, and covered land and water alike with thick
ash deposits. 1500 elk and 5000 deer were killed, and as
amany as 7000 big game animals such as brown
bear. 12 Million Salmon and Chinook fingerlings
(small fish) died as the lakes acidified and boiled,
and over 40 000 mature salmon were forced to flee
the waters through turbines they normally swam
over.
In terms of issues to populations, poor visibility
closed several airports in Washington state, Inter-
state 90 was closed for two weeks, 1000 commer-
cial flights were cancelled. Sewerage and water sys-
tems were clogged, with many local businesses clos-
ing for the duration.
Melting of the summit glaci-
ers—fed theinitial lahars which
started in the summit zone at
around 90MPH slowing to
3KMPH 30 km away. These
flows moved upstream along
the Cowlitz river by 27 miles, in
a 4m high wall of muddy water
The mountain streams and
brooks—becoming clogged
with ash
In total the lahars were responsible for
some major damage including de-
stroying 27 bridges, 298km of high-
ways, 25km of railways and stranding
31 ships in the Columbia River whose
depth was reduced from 12 to 4m.
One of the most significant hazards
during and after the eruption was the
generation of lahars. These came
from several sources and were used
as an example of what could and in-
deed did happen in the Nevado Del
Ruiz eruption.
Spirit lake– overwhelmed by
the landslide and the lateral
blast, the water boiled killing
all aquatic life and then mobi-
lized the settling ash into a
lahar
Caption describing pic-ture or graphic.
MSH: Lahars
The Primary Impacts
The Huish Volcanologist Special Edition
“The nature of
movement was
eerie.... The
entire mass began
to ripple and
churn up, without
moving laterally.
Then the entire
north side of the
summit began
sliding to the
north”
Keith Stoffel,
Geologist flying
over the eruption
column
Page 2
The eruption phase that started in May
continued actively until October of that
year. There have been numerous phas-
es pf activity since then, but don as
dramatic as the 1980 eruption. The
effects of that day have had reverbera-
tions around the world, and can be split
into distinct groups:
Volcanological:
The eruption ceased by 1982, but there
have been several renewed bursts
since then. There have been 7 domes/
spines since 1980, including the whale-
back, pictured above. These spines
grow and collapse periodically, with the
1987 third dome reaching 900m by
800m. Following the pyroclastic flows
and lahars, ash removal from the state
took 10 weeks and cost $2.2 million.
The flows were still at 300 to 420 De-
grees two weeks after the eruption,
and the interaction of groundwater and
hot deposits caused numerous small
explosions within the flows, continuing
for several months.
Environmental:
Although devastation within the blast
zone was total, all forms of life blown
up, carbonized or buried in ash, recov-
ery speed has taken scientists by sur-
prise. This picture at the bottom of the
page shows the same site in 1988 and
2001, secondary succession has taken
place so rapidly partly due to the na-
ture of the eruption. Unlike basic volca-
noes like Hawaii, the erupted material
was ash and pyroclastics, meaning it
was already broken down into small
fragments, meaning weathering could
take place rapidly. The buried seeds
and bulbs could break through loose
ash and the surrounding intact forests
provided a source of plants that grew
into the damaged area, and birds and
animals transported seeds through drop-
pings into the fertile ash.
Social:
57 people were killed in the eruption, by
the time the blast reached them it
was still 360 degrees Celsius causing
instant asphyxiation. Among those
that died were a National Geograph-
ic Photographer and David John-
ston, a young USGS volcanologist
who was stationed immediately in
front of the bulge. The ridge were
he died has been renamed Johnston
Ridge. Over 200 homes were de-
stroyed completely by the blast, the
loss of homes and land is a signifi-
cant set back to local recovery.
There was a marked increase in depres-
sion and other mental health issues in
the months following the start of recov-
ery
On a more positive side, the information
gained from observing this eruption with
high tech equipment and a range of rele-
vant experts on hand meant that signifi-
cant advances in prediction capability
and monitoring were made. The under-
standing of the lateral blast phenomena
and the lahars produced by the meting of
summit glaciers and snow was used to try
and aid the population of Armero during
the 1985 eruption of Nevado Del Ruiz
(Unfortunately
the advice was
not heeded, and
the Lahars gener-
ated by Glacier
melt killed 23000
people).
The eruption also
led to a significant over hall of most mon-
itoring stations in the Cascades range,
and the CVO (Cascades Volcano Observa-
tory) re-evaluated the status of several
other volcanoes.
Economically:
The most up to date estimate of the costs
of the eruption was $2.74 Billion in 2007
dollars. Congress sent $951 Million to
FEMA the US Army Corps of Engineers
and the Small Business Administration.
Unemployment in the area rose by a fac-
tor of ten a few weeks after the eruption,
and tourism in the region was crippled by
the fact that the Mount Baker camp was
utterly destroyed and access to the area
was restricted . Many conventions and
larger social gatherings were relocated
away from the Washington area.
However, these effects were temporary,
and once the national park was reopened
there was a resurgence of visitors who
had observed the eruption on the news,
attracting an entire new group of volcano
based tourists. This influx still continues
today, in 1987 when the site was reo-
pened to climber, a permit was required
for access to the faces costing $22/day,
and half hour helicopter rides costing
$149 per person give you a guided tour of
the summit.
Mount St. Helens National Volcano Mon-ument, which is run by the U.S. Forest Service and straddles Cowlitz and Skama-nia counties, account for much of Cowlitz County's $90 million annual tourism reve-nue and pump about $15 million a year into Skamania County. About 2,400 jobs in both counties are tourism-dependent.
Educational:
Learning continues apace around the volcano. There were 21 active periods between 1980 and 1990, and a google Scholar search reveals over 20,000 papers written about the eruption.
Long Term Recovery and Impacts
The Huish Volcanologist Special Edition
“half hour
helicopter rides
costing $149 per
person give you a
guided tour of the
summit”
Page 3
Potential for Future Hazards
One of the areas worst affected, that still poses a dangerous risk to the area, is Spirit
Lake. Annihilated by the 1980 eruption, the blast hit the lake, sending water 240m up
the hillside, and blocking the outlet. This led to a 60 m rise in the level of the lake, which
within a month had become devoid of all oxygen and life. Scientists initially despaired
that life would take years to come back, but by 1983, there was more biological activity
than ever before, and fish had returned by 1993.
The risk the lake poses is of overflowing and remobilizing loose ash deposits as cold la-
hars. The outlet was blocked by loose ash and pyroclastic deposits, which being uncon-
solidated, will not hold indefinitely,. To reduce the risk of overflow and lahars, there is
no a drainage tunnel removing water and maintaining a safer lower level.
The other risks relate to periods of renewed activity, there will be lahars following signif-
icant rainfall, and small eruptions related to dome building and collapse. The risk is al-
ways higher over winter and is carefully monitored and managed by hazard mapping and
evacuation routes.
MSH is now one of the most heavily monitored volcanoes in the world. The information
it provides is invaluable for predicting other future eruptions
Geography Department
South Road
Taunton
TA1 3DZ
There is a wealth of information about the vol-
canoes on the web. The best source for infor-
mation is the USGS< who have the dedicated
Cascades Volcano Observatory (CVO):
http://vulcan.wr.usgs.gov/
An interesting comparison can be made by look-
ing at eruptive styles and management on Ha-
waii and in the Cascades, this link takes you to
the Hawaiian Volcanoes Observatory where you
can make detailed comparisons between the
risks posed by acidic composite cones and the
basic effusive activity in the pacific:
http://hvo.wr.usgs.gov/
There is an excellent documentary frequently
on TV called “The eruption of Mt St Helens”
made a camera team dropped in the blast zone
two days after the eruption, who found that
compasses did not work, and the volcano was
still erupting
The other good documentary with excellent
footage is “Seconds from disaster: the eruption
of Mt St Helens”.
Key Questions:
Evaluate the management of this hazard
The eruption of MSH in 1980 had only negative
impacts—to what extent do you agree with this
statement?
Useful Links
Phone: 01823 320800
E-mail: [email protected]
R I C H A R D H U I S H C O L L E G E